The present invention relates generally to air filters from environmental air recirculating systems, and more particularly to a process for forming odor absorbent environmental air filtration media.
It has long been the practice in environmental air recirculating systems to use substances such as activated carbon, activated alumina, and the like for odor removal. Proposals have been made to adhere such substances to fibrous air filtration media so that a single filter element can simultaneously perform the dual functions of odor and particulate removal.
One problem which has been encountered in efforts to implement such proposals is that of properly distributing a sufficient quantity of odor absorbent material among the fibers of filter media for bonding thereto. A sufficient quantity of absorbent material must be adhered to the fibers if the filter is to be effective in absorbing odors, and effecting a controlled distribution of the absorbent material among the fibers has been difficult to achieve.
Efforts to distribute and bond dry particulate odor absorbent materials such as small particles of activated carbon among the fibers of a mat have resulted in the creation of such large quantities of dust and "fallout" as to prohibit their gaining commercial acceptance. Attempts to overcome the dust problem have included such proposals as the pretreatment of carbon particles with wetting agents and the like. These pretreating steps are not only expensive to carry out but also tend to reduce the odor absorbing effectiveness of the particulate due to the wetting agent's being absorbed by the particulate.
Still another problem with previous proposals has been that of obtaining high speed filter production. Where dry particulate odor absorbent materials have been used, the problems of dust and effecting proper particulate distribution and bonding have inhibited efforts to obtain high speed production.
One problem that has been addressed with success in the prior art is that of forming a mat of fibrous filter material. Mats of randomly overlaid fibers are readily produced by a commercially available apparatus known in the art as a "Rando-Webber" machine, manufactured by Curlator Corporation, Rochester, N.Y. Another commercially available mat forming apparatus is known as a "Garnett Machine". Mats manufactured by such machines may include man-made or natural fibers, or both, customarily including matting of variable deniers and densities and may be treated with binders, adhesives, tackifiers, plasticizers, flame-retardants, stiffeners and the like as is desired to provide a media suitable for filtering recirculated environmental air in homes, offices and the like. Filtration characteristics of the media are determined by the fiber size, and the density and thickness of the mat, and the type of additives adhered to the fibers.
Another problem which has been addressed with adequate success in the prior art is that of providing bonding agents which can be used to adhere odor absorbent materials to the fibers in a mat. In some instances, substances which are used to treat fibrous mats to stiffen them and to hold their fibers in place remain tacky long enough to serve the additional function of helping to bond absorbent materials to the fibers. In other instances, additional commercially available bonding agents may be applied to the fibers to assure good bonding of odor absorbent particles.